A variety of additive fabrication techniques exist to reproduce essentially any three dimensional structure with a desired exterior. However, for a structure with a given exterior, there are many, and potentially infinite, ways to fill enclosed, interior volumes, a process generally referred to as in-filling. For example, one can fill the entire volume with build material, which may produce a maximally durable structure but takes longer to build and uses more material than other alternatives. Alternatively, one can forego filling the structure's interior with any build material at all. This leads to a minimum use of build material and a reduction in build time, but may produce a highly fragile structure.
Existing solutions to in-filling generally rely on simple geometric patterns such as a square grid, along with a few simple approaches to boundary conditions where the simple geometric pattern does not match an exterior wall. There remains a need for improved in-filling techniques for additive fabrication.